The present invention relates to an additive that when blended with petroleum oils in low concentration, the tendency of the oil to foul and coke surfaces is reduced. This is achieved by increasing the solvency of the asphaltenes, the least soluble fraction, in the petroleum oil.
It is well known that petroleum crude oils and asphaltene containing oils derived from petroleum crude oils have the tendency to deposit organic solids, called foulant and coke, on refinery process equipment that contact the oil. Such process equipment include, but are not limited to, pipes, tanks, heat exchangers, furnace tubes, fractionators, and reactors. Even small amounts of foulant or coke results in large energy loss because of much poorer heat transfer through foulant and coke as opposed to metal walls alone. Moderate amounts of foulant and coke cause high pressure drops and interfere with and make process equipment operate inefficiently. Finally, large amounts of foulant or coke plug up process equipment to prevent flow or otherwise make operation intolerable, requiring the equipment to be shut down and cleaned of foulant and coke.
It is also well known that petroleum derived, asphaltene containing oils that have undergone reaction at high temperatures, above 350.degree. C., have a tendency for rapidly fouling process equipment, either on cooling or by blending with a more paraffinic oil. Such processed oils include, but are not limited by, the highest boiling distillation fraction after thermally or catalytically hydrothermally converting atmospheric or vacuum resid of petroleum crude and the highest boiling fraction of the liquid product of fluid catalytic cracking, called cat cracker bottoms or cat slurry oil or decant oil. This rapid fouling is caused by asphaltenes that become insoluble on cooling or on blending with a more paraffinic oil. Here asphaltenes are defined as the fraction of the oil that is soluble when the oil is blended with 40 volumes of toluene but insoluble when the oil is blended with 40 volumes of n-heptane. If the asphaltenes become insoluble at high temperatures, above 350.degree. C., they rapidly form toluene insoluble coke (see I. A. Wiehe, Industrial & Engineering Chemistry Research, Vol. 32, 2447-2454). However, it is not well known that the mere blending of two or more unprocessed petroleum crude oils can cause the precipitation of insoluble asphaltenes that can rapidly foul process equipment or when such crude oil blends are rapidly heated above 350.degree. C., the insoluble asphaltenes can coke pipestill furnace tubes. If the blending of oils causes the precipitation of asphaltenes, the oils are said to be incompatible as opposed to compatible oils that do not precipitate asphaltenes on blending. Thus, incompatible blends of oils have a much greater tendency for fouling and coking than compatible oils. If a blend of two or more oils have some proportion of the oils that precipitate asphaltenes, the set of oils are said to be potentially incompatible. Fortunately, most blends of unprocessed crude oils are not potentially incompatible. It is only for that reason that many refineries can process petroleum crudes for long times without the need to shut down and clean out foulant and coke. Several crude oils have even been identified that are self incompatible. That is they contain insoluble asphaltenes even without blending. Nevertheless, once an incompatible oil or blend of oils is obtained, the rapid fouling and coldng that results usually requires shutting down the refinery process in a short time. This results in a large economic debit because while the process equipment is cleaned, large volumes of oil cannot be processed.
Therefore, it is desirable to increase the solubility of the asphaltenes in the crude oil. This can be achieved by adding asphaltene dispersants to the crude oil.